1. Field of the Invention
The invention relates generally to devices and methods for decreasing erosion damage to pumping components during downhole fracturing operations and for extending the life of the equipment used. In particular aspects, the invention relates to the composition of proppants used in fracturing operations.
2. Description of the Related Art
Fracturing operations are used to improve the flow of hydrocarbons from a subterranean formation and into a wellbore. Fracturing involves pumping of a fracturing fluid into the wellbore under extremely high pressure in order to induce fracturing in the formation rock immediately surrounding the wellbore. Fracturing increases the porosity in the formation and allows freer transmission of hydrocarbons through the formation and into the wellbore. Proppants are often included in the fracturing fluid. Proppants are generally particulate matter that is carried in a fracturing fluid. The proppant particles will reside within the small cracks and crevices of the formation that are created by the fracturing fluid, effectively permitting freer flow of fluids to continue after the fracturing agent is no longer pumped down the wellbore under pressure.
Currently, attempts are being made to increase the lengths of the zones that can be fractured and packed with proppant (i.e., increased zone lengths of about 300-400 feet are being considered). This increase in length dictates raising the treatment pump rate and proppant volume to be able to treat these lengthened zones. Unfortunately, increasing pump rate and proppant volume has significant deleterious effects upon the pumping components, including fluid conveying tubing, surface lines, chokes, manifolds, work strings, valves, and the downhole gravel pack liner assembly. Conventional proppants are extremely erosive and create tremendous wear upon pumping equipment during use. Erosion is usually a function of flow velocity and the amount of abrasive material being flowed. The erosion rate increases in direct correspondence with an increase in proppant volume (i.e., doubling the amount of proppant doubles the erosion rate). However, doubling the pump rate will increase the amount of erosion by a factor of four. As a result, operations that require both increased proppant amounts and increased flow rates are particularly problematic.
The components that tend to suffer the most severe damage during pumping of proppants are portions of the cross-over tool, including the cross-over port, cross-over housing, and lower extension. The casing and other elements on the gravel pack liner assembly where changes in interior casing diameter will also demonstrate significant wear.
To date, the conventional wisdom has been that measures taken to reduce erosion damage caused by the proppant might also tend to reduce the effectiveness of the proppant in the formation. For this reason, the inventors believe that they have not been used in conventional hydraulic fracturing operations or fracture packing operations wherein they are run through a cross-over tool. Instead, resin-coated proppants have been used primarily in hydraulic fracture stimulation treatments.
Resin-coated proppants are known materials. A coating method is described, for example, in U.S. Pat. No. 4,494,318 issued to Smillie. Further, such resin-coated proppants are available commercially from suppliers such as Santrol and Borden Chemical. However, conventional resin-coated proppants are not coated with the goal of reducing erosion and, as a result, do not perform this function optimally. Most conventional coatings are designed to provide improved strength to the proppant substrate, thereby, increasing the strength of the proppant particle within the formation fracture. Alternatively, coatings are engineered to permit the individual proppant particles to bond together to help control proppant flowback, which might occur as production fluid is flowed into the wellbore at an increased rate. An example of this type of proppant is described in U.S. Pat. No. 5,604,184 issued to Ellis et al.
The present invention addresses the problems of the prior art.